Signal translating apparatus



April 2, 1946. v

Filed Julie 5, 1944 i.

Egl

@MWL

Gttorncg Patented Apr. 2, 1946 SIGNAL TnANsLArING APPARATUS Ren Snepvangers, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporan tion of Delaware o Application June 5, 1944, Serial No. 538,834 v11 Claims. (Cl. 179-100.41)

" This invention relates to signal translating apparatus, and more particularly to a signal translating device of the capacity type adapted for use especially in connection with phonograph records, the present invention being in the nature of an improvement over that disclosed and claimed in the copending application l f Chester M. Sinnett, Serial No. 414,305, led October 9, 1941, now Patent No. 2,376,456,\granted May 22, 1945, andassigned to the Radio Corporation of America.

In the aforesaid copending application,v there is disclosed av capacity type pickup which comprises a supporting member carrying a pair of electrodes in capacitative relation to each other, one of the electrodes being stationary and the Iother being.

mounted on an expansible framework for vibratory movement relative to the stationary electrode. The movable electrode consists of a relatively thin, narrow, flexible strip of metal extending across the stationary electrode in spaced relation thereto, the flexible strip being anchored at both its end on the aforesaid framework. A needle is secured to the movable electrode sub- Aside from the foregoing, the resonant frequency i or vibration of the. flexible strip is controlled by expanding the expansible framework on which it is mounted. Since the vibratory ribbon oristrip is under great tension, it becomes set in its stretched condition after a period of use, and itis again necessary to slightly expand the framework. The arrangement in the particular forms of pickup devices disclosed in the aforesaid co pending application is such that, upon continued expansion of the `framework, the length of ribbon which cooperates with the stationary plate or electrode is increased, and this has the effect of lowering the resonant frequency' of the vibrastantially midway between its ends and is arranged to cooperate with the groove of a phonograph record. Movement of the movable electrode in response to the needle is conned substantially to a region-in the vicinity of the needle i a suitable high frequency oscillator (for example,

a 40 to 50 megacycle oscillator), and when the capacity of the pickup is varied in response to the record, it produces a frequency shift in the oscillator circuit, and frequency modulation results. The frequency modulated signal may be passed through a suitable F-M channel for conversion into amplitude modulated signals and 'reproduction in known manner.

The particular forms of pickup disclosed in the aforesaid copending application of Sinnett, while highly satisfactory in use, involve diiilculties in manufacture. Among other things, extreme care must be exercised during manufacture to insure that the vibratory strip and the fixed electrode plate with which it cooperates will always remain in parallel relation.- In practice, it has been found that this relation is occasionally disturbed after the pickup has been ln useY or some time.

tory strip quite considerably.

The primary object of my present invention is to provide an improved pickup device of the type set forth above which will be free from the aforementionedlimitations.

More particularly, it is an object of my present invention to provide an improved capacity type pickup which is extremely simple in construction, which can be easily manufactured without requiring critical adjustments or extreme care during manufacture, and which is inexpensive in cost.

Another object of my present invention is to provide an improved capacity type pickup as above set forth wherein the tension appliedto. the vibratory electrode may be varied without varying either the air gap between the two electrodes of the capacitor or the length of the vibra tory portion of the ribbon.

A further object of my present invention is to provide an improved capacity type pickup wherein the natural period of the vibrating electrode can be maintained substantially constant regardless of the degree of tension applied thereto within the operating range.

Still another object of my present invention is to provide an improved capacity type pickup as above set forth which will afford a comparativel large gain in signal to noise ratio.

A further object of myA present invention is to provide an improved capacity type pickup which is especially useful in connection with phonograph records, which will not cause .the record with which it cooperates duringl reproduction to radiate extraneous sounds, and which will not itself produce such sounds. 1

Still a further object of my present -invention is to provide an improved capacity type pickup which' will operate with a minimum of distortion.

Another object of my present invention is to provide an improved capacity type pickupolasV I above set forth in which the mass of the moving parts is very low. l

Still another object of my present invention is to provide an improved capacity typey pickup which is very flexible in operation.

It is also an object of my present invention to provide an improved capacity type pickup as above set forth which is sturdy in construction, th'e parts of which are easily accessible, which will have a long life, and which' is highly veflicient in use. n

In accordancewith my present invention, I provide a yoke-shaped supporting member ter.- minating in a pair of forwardly' extending arms across the ends of which I mount the vibratory, conductive ribbon of resilient material. Between the yoke arms, there-is pivotally mountedfor swinging movement toward and away from` the vibratory ribbon a block of insulating material which has extending from its surfabe facing the ribbon a pair of spaced projections adapted to engage the ribbon. lBetween the aforesaid projec- 1 tions, the insulating block carries a plate electrode ,for cooperation with the vibratory ribbon. An adjusting screw is mounted on the supporting yoke in position to engage the insulating block to move it toward 'the ribbon so that the projections on the block will engage the ribbon and thus determine the size of the air gap between the two electrodes. Continued adjustment of the block toward the ribbon will then cause the projections thereof -toextend beyond the ends of the yoke arms and thus apply more or less pressure to the resilient ribbon. However, since the projections have a xed dimension andare spaced from each other on a fixed distance, it is apparent that neither the spacing between the electrodes nor the length of ribbon between the two projections will be altered regardless of the pressure applied to the ribbon. The resonant frequency of the vibratory ribbon is usually around 15.000 cycles per second, and since the tension of the ribbon is great, the length of the vibratory portion thereof appears to be the controlling factor which governs its natural period rather than the variation in tension thereof resulting from slight adjustments of the block on the supporting yoke. As a result. should the ribbon become set in its ad- Justed position, it is merely necessary to project the block forwardly a slight bit more to apply suitable tension to the ribbon without altering the length of the vibratnry portion thereof, and hence without materially altering lits natural period.

The novel features that I consider characteristic of my invention are set forth with particularityin the appended claims. The invention itself. however, both as to its organization and method of operation, as well as additional objects andadvantages thereof, will best be understood from the following description of one embodiment thereof. when read In connection with the accompanying drawing. in which Figure l is a perspective view of a pickup device constructed. according to my present invention and with the cover thereof removed,

Figure 21s a sectional view taken substantially along the line II-II of Fig. 1. and

Figure 3 is a sectional view taken along the line III-HI 0f Fig. 1.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown aseases ings 5 useful for connecting the supporting member I` to a suitable pickup arm (not shown). A strip1 of resilient, conductive material has its ends clamped against the shoulders 4 by blocks 9 which are secured to the yoke member I by screws II. The conductive strip or ribbon 11's made of exible and resilient material and isso mountedon the supporting yoke I that it extends around the curved, forward ends of the yoke arm 3 and spans the space therebetween. The ribbon 1 may be made of nickel-steel alloy or of any other suitable material having a thickness of aboutV 2 or 3 mils and a width of about 11s to about :Pz inch. 'Ihese dimensions are not critical, however, and maybe varied to suit particular require'- ments.

Pivotally mounted on the supporting yoke i between the arms 3 thereof, as by means of a pin or shaft I 3. is a block I5 of insulating material, such as Bakelite or the like. 'I'he block I5 is mounted for swinging movement toward and away from the portion of the ribbon which spans the space between the yoke arms 3 and is provided with a pair of spaced, forwardly extending projections l1 adapted to engage the ribbon 1. The block I5 also carries between the projections i1 a conductive plate of copper, brass, or the l'ke I9 which is arrangedlto cooperate with the ribbon 1. h

An adjustable screw 2l on the block I bears against the rear face of the block I5 and is adjustable to swing the block I5 forwardly in order to bring the projections I1 into engagement with the ribbon 1. This determines the spacing, or width of the air gap 23 between the ribbon 1 and the conductive `plate I9, which' may be of the order of 3 mils. Continued adjustment of the screw 21 in a forward direction after the proections I-1 have engaged the ribbon will cause the projections I1 to be moved forwardly of the asupportlng yoke I which may be of brass or in Fig. 2, and more or less pressure is then applied by theiprojections I1 against the. ribbon 1 to place the ribbon under tension. On the other hand, when the screw 2l is backed away somewhat. the ribbon 1, due toits resilience, will cause the block IES to move back with the screw 2l until the ribbon is again in engagement with the forward ends of the yoke arms 3. It will be apparent that the width of the air gap 2 3 remains constant regardlessof the degree of tension applied to the ribbon 1. Also, since the distance between the projections I1 remains constant. it is apparent that the length of the vibrators' portion of the ribbon 1 between the projections I1 will also remain constant, and therefore its natural period will remain-substantially constant regardless of the tension-applied thereon within well known limits,

of course.

Secured to the upper portion of the front face of the 'block I5 is an anchoring plate 2B to which the upper en d of a needle 21 of plano wire or the like may be secured, as by solder 29. swaging, or in any other suitable manner. The vertical shank oi' the needle 21 is also soldered to the ribbon 1 by a solder connection 3|. Below the ribbon 1, the needle 21 has a right angled bend and terminates in a, holder 33 which carries a tip 35 of Sapphire or the like adapted to engage in and cooperate with the groove of a phonograph record. During operation. the record groove rides v under the needle tip 35 and causes the needle to I9 and the ribbon 1.

vibrate. In turn, the needle 21 imparts vibratory movement to the-ribbon 1 relative to the iixed or stationary plate I9 to thereby vary the capacitance of the capacitor 1, I9. Connection is preferably made from this capacitor to a suitable transmission line (not shown) one conductor of;

which is preferably grounded and connected to the supporting yoke I with which the vibratory ribbon 1 has electrical connection, and the other or high potential conductor of which is connected by a lead 31 to the stationary plate I9. The output of the pickup device may then be connected across a tuning inductor in the input circuit of a suitable vacuum tube oscillator which has been tuned to a desired mid-frequency to thereby provide frequency modulated signals in a manner more fully set forth and claimed in a copending application of Chester M. Sinnett, Serial No. 459,375, iiled September 23, 1942, and also assigned to the Radio Corporation of America. Y

From the foregoing description` it will be apparent to those skilled in the art that I have provided an improved capacity type pickup which is extremely simple in construction,rwhich has a minimum of operating parts. and which can be easily fabricated and assembled. The block I5 and its conductive plate I9 can be machined easily to insure desired parallelism between the plate This relation is always maintained after assembly of the parts and regardless of the pressure applied to the ribbon 1.

At the same time, the air gap 23 remains constant irrespective of the position to which the block I5 has'been adjusted. and the resonant fre.-

quencv of the vibratory portion of the ribbon 1 remains substantially constant because the length of the portion thereof between the projections I1 remains constant.

Although I have shown and described only a. single embodiment of my invention,` it will undoubtedly be apparent to those skilled in the art that many yother forms thereof, as Well as changes in the particular one described, are possible. For example, the block I5 may be slidably mounted on the yoke I instead of being mounted for swing ing movement relative to the ribbon 1Q Again,

adjustment of the block I5 may be effected by means of a suitably formed cam, instead of by the adjusting screw 2|. Other changes 'of a similar nature will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by the priorl art and by the spirit of the appended claims.

I claim as my invention:

l. A phonograph'record signal translating device comprising a support, a yieldable conductive member vibratively carried by said support, a member of insulating material movably mounted on said support for adjustment thereon relative to said vibrative member, a second .conductive member carried by said insulating member in cooperative relation to said vibrative member,

means movable with said insulating member for maintaining said vibrative member in predetermined spaced relation to said second conductive .2. A phonograph record signal translating;deff?.VH Y

vice comprising a support, a yieldable conductive member of insulating material movably mounted on said supportfor adjustment thereon relative to said vibrative member, a second conductive member carried by said insulating member in cooperative relation to said vibrative member, y

means extending from said insulating member toward and adapted to engage said vibratory member to maintain said conductive members in predetermined spaced ,relation to each other, said conductive members having a dielectric therebetween and constituting a capacitor, means for adjusting said insulating member on said support to bring said iirst named means into engagement withsaid vibrative member and thereafter-to cause said first named meansto apply while maintaining the spacing between said conductive members constant,and a needle carried4 insulating member comprises a pair at spaced.

tions, one adjacent each end of said second conthat the length of the portion of said vibrative member between said projections remains con`1 stant regardless oi the pressure applied thereto.

5. A signal translating device according to claim 2 wherein said insulating member is pivotally carried by said support for swinging movement thereon in relation to said vibrative member.

6. A signal translating device according to claim 2 characterized in that said support is convstituted by a yoke having a pair of spaced arms,

and characterized further in that said insulating member is carried thereby between said arms.

7. A signal translating device accordingto claim 2 characterized in that said support is constitutedby a yoke having e. pair of spaced arms, characterized further in that said insulating member is carried thereby between said arms for g5 adjustment toward the ends of said arms to positions where said extending means will project beyond the ends o f said arms, and characterized further in that said vibrative member extends across the space between said arm ends inthe path of movement of said extending means.

8. In a phonograph record signal translating device, the -combination oi' a support comprising a yoke terminating in a pair o1' spaced arms, a resilient conductive strip .mounted on said yoke -across the ends oi' said arms-whereby to span member vibrativelycarried by said support, ay

more or less pressure to said vibrative memberv ductive member, and characterized further in the space therebetween, a block of insulating material movably carried by said yoke between said arms for movement toward and .away from said strip, a conductive plate carried by said block for cooperation with said strip, a pair of projections on said block, one adjacent each end of said plate, extending toward said strip, said projections maintaining said plate spaced a predetermined distance-from said strip when they engage said strip, and means associated with said block for bringing said projections into engagement with said strip and forthereafter causing said projections to applyA more or less pressure to said-strip without altering either the spacing between said strip and said plate or the length of the portion of said strip between said projections.

9. The invention set forth in claim 8 characterized in that said block is pivotally mounted on said yoke for swinging movement relative to said strip.

10. A phonograph record signal translating device comprising a yoke terminating in a pair of spaced arms, a conductive 'strip vibratively mounted on said yoke across the ends of said arms whereby to span the space therebetween, a block -of insulating material pivotally carried by said yoke between said arms for swinging movement toward and away from said strip, a conductive plate carried by said block for cooperation with A said strip. a pair of projections on said block,

one adjacent each end of said plate, extending toward said strip, said projections maintaining said plate spaced a predetermined distance from said strip when they engage said strip, said strip andl plate then having an air space therebetween to constitute a capacitor, means associated vwith said block for bringing said projections into engagement with said strip to provide said capacitor, and a needle carried by said strip for cooperation with a record, the movement of said needle in response to the record imparting vibratory motion to vsaid strip relative to said plate to thereb'y correspondingly vary the capacitance of said capacitor.

11. A signal translating device according to v claim 10 characterized in that said strip is of resilient material, and characterized further in that the means associated with said block comprises a member adjustably carried by said yoke in cooperative relation to said block and adjustable on said yoke-to cause said projections to apply more or less pressure against said strip after being brought into engagement with said strip without, however, altering either the space bertween vsaid strip and saidplate or the length of that portion of said strip between said projections. 1

REN SNEPVANGERS. 

